JPH11177134A - Manufacture of semiconductor element, semiconductor, manufacture of light emitting element, and light emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simplify a complicated process by removing hydrogen immediately below an electrode by performing annealing after an electrode is formed, by forming the electrode as a hydrogen permeating electrode by using Pd and obtaining a good ohmic contact between a metal and a semiconductor by forming an electrode on the cleans surface of GaN which has not been subjected to any high-temperature process, and then, by reducing the number of performing times of high-temperature processes in an element manufacturing process to one time. SOLUTION: After an Si-doped n-type GaN layer 102 is formed to a thickness of 4 μm on a C-face of a sapphire substrate 101 by using an MOCVD device, a GaN film 103 doped with Mg to an impurity concentration of about 1×10<20> cm<-3> is grown on the layer 102 to a thickness of 1 μm. Then a Pd electrode 104 which is a hydrogen permeating electrode is formed to a thickness between 40 Å and 1 μm on the clean surface of a nitride gallium semiconductor before the semiconductor is subjected to annealing which is performed for changing the polarity of the semiconductor to the p-type. Then the semiconductor is annealed for 10-minutes at 700 deg.C in an inert gas atmosphere of nitrogen, argon, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for converting a gallium nitride-based compound semiconductor doped with a p-type dopant into a p-type and a process for forming a device.

[0002]

2. Description of the Related Art The process of a conventional gallium nitride-based compound semiconductor light emitting device will be briefly described. FIG. 4 shows a schematic diagram of a process conventionally used. On a sapphire substrate 401, an n-type layer 402, a light emitting layer (active layer) 403, p
After forming a GaN-based compound semiconductor in the order of the mold layer 404,
A first heat treatment (p-type annealing) is performed to reduce the resistance of the layer doped with the p-type dopant. In a p-type layer of a gallium nitride-based semiconductor doped with Mg or the like as a p-type dopant, when a dopant such as Mg is deposited, H _{2 of} a carrier gas or hydrogen 405 of NH ₃ of a reaction gas is used.
And electrical compensation is provided, so that the resistance of the p-type layer is large. Therefore, H is separated from H by Ga.
The p-type layer must be released outside the N film to lower the resistance, and this p-type annealing step is required.
(See FIG. 4A.) This p-type annealing step is usually 80
This is performed at a high temperature of about 0 ° C. for about 10 minutes. After that, RIE
Exposing the n-type layer, the n-electrode 407 and the p-electrode 4
Second heat treatment after alloy formation (alloy treatment)
Is carried out. (See FIG. 4B.) This is a step for alloying the semiconductor and the metal to lower the contact resistance. As described above, a total of two high-temperature processes (p-type annealing and alloying) were required for device fabrication.
It is also known that when annealing a p-type dopant-doped gallium nitride-based semiconductor into p-type, hydrogen bonded to Mg as a p-type dopant cannot pass through the electrode immediately below the electrode, so that resistance cannot be reduced. (JP-A-6-23
For this reason, in the order of the process, the electrodes are formed after the p-type annealing as described above.

[0003]

Since the p-type annealing is usually a high temperature process of 700 ° C. or more, the re-evaporation of nitrogen near the surface of the gallium nitride-based semiconductor causes a good electrode formation after the above process. There was a problem that ohmic contact could not be obtained. In addition, two high-temperature processes are required in the device fabrication process, which complicates the process. At the same time, due to the difference in lattice constant and coefficient of thermal expansion between the sapphire substrate and the gallium nitride-based semiconductor, film expansion due to repeated high-temperature processes. Crystal defects in the semiconductor layer,
There has been a problem that dislocations, cracks and the like are generated, and the luminous efficiency is reduced. An object of the present invention is to solve the above problems.

[0004]

According to a first aspect of the present invention, there is provided a method of manufacturing a semiconductor device, comprising: forming a hydrogen-permeable electrode on a surface of a high-resistance gallium nitride-based compound semiconductor doped with a p-type dopant; A heat treatment is performed to obtain a p-type layer.

[0005] A semiconductor element according to a second aspect of the present invention is a semiconductor element manufactured by the manufacturing method according to the first aspect, wherein a main constituent material of the hydrogen permeable electrode is Pd. .

According to a third aspect of the present invention, in the semiconductor device, the hydrogen-permeable electrode has a two-layer structure, and a side in contact with a high-resistance gallium nitride-based compound semiconductor doped with a p-type dopant is a Pd electrode; A metal electrode is provided on the electrode, and the thickness of the metal electrode is 20 to 200 mm.

In the light emitting device according to the fourth aspect of the present invention, an n-type layer of a nitride-based compound semiconductor, a light-emitting layer, and a p-type layer are formed in this order on a substrate, and a main constituent material is formed on the p-type layer. Forming a hydrogen-permeable electrode of Pd, forming an electrode pad made of a material that does not transmit hydrogen on a part of the hydrogen-permeable electrode, and then performing thermal annealing at a temperature of 600 ° C. or more and 900 ° C. or less. Features.

A light emitting device according to a fifth aspect of the present invention is a light emitting device manufactured by the manufacturing method according to the fourth aspect, wherein the hydrogen permeable electrode is composed of two or more layers, and a p-type semiconductor. Is a Pd electrode, the metal film thickness on the Pd electrode is 20 to 200 °, and the total film thickness of the Pd electrode and the metal film is 40 to 400 °.

According to the above-described manufacturing method, an electrode can be formed on a clean GaN surface which has never undergone a high-temperature process. Further, by using a specific electrode, it is possible to form p-type GaN having low resistance by transmitting hydrogen immediately below the electrode by p-type annealing after forming the electrode. In addition, thermal annealing for obtaining ohmic contact between the semiconductor and the electrode can also be performed. For this reason, the number of high-temperature processes in the device fabrication process can be reduced to one.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on specific embodiments. (Embodiment 1) FIG.
FIG. 3 is a schematic structural view showing an N semiconductor light receiving element. 101 is a sapphire substrate, 102 is an n-GaN layer, 103 is a Mg-doped GaN layer, and 104 is a hydrogen permeable electrode Pd.

First, an MO was placed on the sapphire substrate 101C.
After the Si-doped n-GaN layer 102 is grown to a thickness of 4 μm using a CVD apparatus, the impurity concentration becomes 1 × 10 ²⁰ c.
The GaN layer 103 doped with Mg to about m ⁻³ is 1 μm
It grows with the film thickness of. A hydrogen permeable electrode Pd electrode 104 is formed on the surface of the clean gallium nitride-based semiconductor before the p-type annealing, in a thickness range of 40 ° to 1 μm. Then, in an inert gas atmosphere such as nitrogen or argon,
Thermal annealing is performed at 00 ° C. for 10 minutes. At this time, the relationship between the Pd film thickness and the resistivity of p-GaN is shown by a graph in FIG. At this time, Pd is a hydrogen-permeable electrode, and hydrogen 10 in the gallium nitride-based semiconductor immediately below the Pd electrode.
Since 5 passes through the electrode, it was found that the Mg-doped GaN layer can be made into a low-resistance p-type. The resistivity is 1.2 Ω · cm, and the same characteristics as the conventional case are obtained. The contact resistance between the semiconductor and the metal is also 3 × 10 ^-3 from the conventional 1 × 10 ⁻² Ω · cm ^2. Ω · cm ² , and good ohmic contact has been obtained. At this time,
Within the above range of the film thickness, a p-GaN film having a low resistance was obtained irrespective of the film thickness of Pd as the hydrogen permeable electrode. If the film thickness is less than 40 °, good ohmic contact cannot be obtained, and if it is 1 μm or more, hydrogen cannot pass therethrough, so that the resistance of the Mg-doped GaN layer cannot be reduced.

The thermal annealing temperature is 400 to 1
The experiment was performed in the range of 000 ° C. It was found that p-GaN with low resistance was obtained between 600 and 800 ° C., and that ohmic contact with the metal electrode was obtained. As a result, an electrode can be formed on a clean p-GaN surface before thermal annealing, and good ohmic contact can be obtained.

Embodiment 2 FIG. 3 is a schematic structural view of a sample used in Embodiment 2 of the present invention. As shown in FIG. 3, a GaN buffer layer 302 is formed on a sapphire substrate 301,
n-type GaN layer 303, n-type Al _0.1 Ga _0.9 N lower cladding layer 304, In _0.2 Ga _0.8 N active layer 305, a thin layer p
Type Al _0.05 Ga _0.95 N evaporation prevention layer 306, p-type Al _0.1
A Ga _0.9 N upper cladding layer 307 and a p-type electrode GaN cap layer 308 are sequentially laminated. Next, an n-type GaN layer 303 is formed by RIBE (reactive ion beam etching).
Is dry-etched until the n-type GaN layer is exposed to form an n-electrode 312 on a part of the exposed surface of the n-type GaN layer. Thereafter, a light-transmitting electrode 309 is formed on a part of the p-type electrode GaN cap layer 308, and an Au electrode pad 310 is formed on a part of the light-transmitting electrode. 311 in the figure is p-Ga
Represents hydrogen in the N layer.

Here, the device forming process will be described in detail. First, the sapphire substrate 301 is heated at 1050 ° C. in an H ₂ atmosphere using an MOCVD apparatus to perform a surface treatment on the substrate. Thereafter, the substrate temperature is lowered to 500 ° C., and Ga
An N or AlN buffer layer 302 is formed. At this time, the thickness of the buffer layer is 250 ° for GaN and 500 ° for AlN. Next, the substrate temperature is raised to 1020 ° C., an n-type GaN layer 303 is grown to about 4 μm, and the n-type Al _0.1 Ga _0.9 N lower cladding layer 304 is grown to 1 μm at the same temperature.
m. Next, the substrate temperature is reduced to 800 ° C., and the non-doped or Si-doped In _0.2 Ga _0.8 N active layer 305 is
It is grown to a thickness of 00 °. Next, the substrate temperature is equal to or higher than the growth temperature of the non-doped or Si-doped In _0.2 Ga _0.8 N active layer 305 and the p-type Al _0.1 Ga _0.9 N upper cladding layer 307 is formed.
About 900 ° C. by thin layer p-type Al _0.05 is the growth temperature below
A Ga _0.95 N evaporation prevention layer 306 is grown. Thereafter, the growth temperature is increased to about 1020 ° C., and the p-type Al _0.1 Ga _0.9 N upper cladding layer 307 is grown to about 1 μm. Next, a p-type electrode GaN cap layer 308 is grown to about 1 μm. At this time, the thin p-type Al _0.05 Ga _0.95 N evaporation preventing layer 306 becomes a high quality film while the substrate temperature is raised to 1020 ° C. Thereafter, in order to form the n-electrode 312, a resist is applied and patterned, and a portion of the grown semiconductor layer is removed by dry etching to expose the n-type GaN layer 303. A film thickness of 3 on the n-GaN layer in the order of Ti and Al
An n-electrode 312 is formed by vapor deposition at 00 ° and 8000 °.
Next, a hydrogen-permeable electrode Pd is deposited to a thickness of 50 ° to form a light-transmissive electrode 309, and an Au electrode pad 310 is formed on a part of the light-transmissive electrode 309 with a layer thickness of 8000 °.

After the electrodes are formed, thermal annealing is performed in an inert gas such as nitrogen or Ar at 600 to 900 ° C. for 1 to 30 minutes. This thermal annealing realizes a low resistance p-type of the p-type layer of the gallium nitride based semiconductor and a low contact resistance of the p-electrode in one heat treatment at the same time.
By controlling the layer thickness of the translucent electrode to the value shown above, p-GaN separated from Mg by thermal annealing
Hydrogen 311 in the layer can pass outside the GaN film, and the p-type layer 313 in a region where there is no Au electrode pad on the top
Can be selectively reduced. Since the Au electrode is very thick, hydrogen in the gallium nitride-based semiconductor immediately below the Au electrode cannot pass through the Au electrode, and the p
The mold layer remains at a high resistance. Through the above-described process steps, the resistance immediately below the Au electrode pad is high, and A
A low-resistance film can be formed on the translucent electrode portion without the u pad. Finally, an LED chip is formed by dicing.

FIG. 2 is a graph showing the relationship between the total thickness of Pd / Au and the resistivity of p-GaN when the translucent electrode portion has a two-layer structure of Pd / Au. It is a graph represented by. In this case, the thickness of Pd is constant at 40 °, and the thickness of Au is changed from 0 to 4000 °. When the thickness of Au is up to 160 °, the resistivity of p-GaN is about 50 Ω / cm ² , and when Au is as thin as 160 ° or less, hydrogen in p-GaN passes through the Pd / Au electrode and p-GaN has a low resistivity. It turns out that it becomes resistance. But Au
When the film thickness is more than 160 °, p-GaN has high resistance. Similar results were obtained even when the metal on Pd was different from Ni and Pt. Further, at 800 ° C. for the Pd / Au electrode,
Contact resistance after thermal annealing for 0 minutes is 1 × 10 ^-3 Ω
・ Cm ² , and good ohmic characteristics can be obtained. By forming the light-transmitting electrode in two layers,
It was found that the problem of oxidation in the high temperature process of d can be avoided.

In the above embodiment, Pd is used as the material of the hydrogen-permeable electrode. However, the same effect can be obtained even if Pd is used as a main component and other metals are mixed at a ratio of about 10%. It was confirmed that it could be done. In this case, by mixing a highly reactive metal (Ti, Mg, Zn, etc.) into Pd at about 10%, the reaction between Pd and the p-type electrode GaN cap layer 308 as a base during heat treatment is promoted. The effect of increasing the adhesiveness of was obtained.

By performing the above-described process, the current confinement structure can be easily manufactured in a self-aligned manner. Further, since the electrodes are formed before the p-type annealing treatment, nitrogen escape from the surface and contamination with impurities on the film surface can be prevented, and the characteristics of the electrodes are improved. In addition, the high-temperature process (p-type annealing, alloying), which has been required twice, has been reduced to one step.
In this case, the number of times can be reduced, and the damage due to the heat of the film can be reduced while simplifying the process steps.

[0019]

By using Pd which is a hydrogen-permeable electrode, hydrogen immediately below the electrode is released by thermal annealing even after the electrode is formed, so that the electrode can be formed on a clean GaN surface that has not undergone a single high-temperature process. Good ohmic contact between metal and semiconductor is obtained. In addition, since the number of high-temperature processes in the device fabrication process can be reduced from two to one, complicated processes can be simplified, and damage to the film due to the high-temperature process can be reduced. Furthermore, by forming a portion using a Pd electrode and a portion using another electrode on the GaN surface,
The gallium nitride-based compound semiconductor layer doped with a type dopant can be selectively made p-type, and for example, a current confinement structure can be formed. The effect as described above can be obtained even when an electrode thinned to a certain film thickness or less is used instead of the hydrogen permeable electrode Pd as described above.

[Brief description of the drawings]

FIG. 1 is a schematic structural diagram of a hydrogen-permeable electrode Pd formed on p-GaN according to an embodiment of the present invention.

FIG. 2 shows the resistivity and G of Mg-doped GaN after thermal annealing.
5 is a graph showing a relationship with the thickness of an electrode formed on aN.

FIG. 3 is a schematic structural view of an LED according to an embodiment of the present invention.

FIG. 4 is a schematic view of a conventional LED structure.

[Explanation of symbols]

Reference Signs List 101 sapphire substrate 102 n-GaN layer 103 Mg-doped GaN layer 104 Pd electrode 105 hydrogen 301 sapphire substrate 302 GaN buffer layer 303 n-type GaN layer 304 n-type Al _0.1 Ga _0.9 N lower cladding layer 305 In _0.2 Ga _0.8 N Active layer 306 Thin p-type Al _0.05 Ga _0.95 N evaporation preventing layer 307 p-type Al _0.1 Ga _0.9 N upper cladding layer 308 p-type electrode GaN cap layer 309 translucent electrode 310 Au electrode pad 311 in p-GaN layer Hydrogen 312 n-electrode 313 p-type layer

Claims (5)

[Claims] 1. A method for manufacturing a semiconductor device, comprising: forming a hydrogen-permeable electrode on the surface of a high-resistance gallium nitride-based compound semiconductor doped with a p-type dopant, and then performing heat treatment to obtain a p-type layer. 2. A semiconductor device manufactured by the manufacturing method according to claim 1, wherein a main constituent material of the hydrogen-permeable electrode is Pd. 3. The hydrogen-permeable electrode has a two-layer structure,
The side in contact with the high-resistance gallium nitride-based compound semiconductor doped with a p-type dopant is a Pd electrode, the upper side of the Pd electrode is a metal electrode, and the thickness of the metal electrode is 20 to 200 °.
The semiconductor device according to claim 2, wherein 4. An n-type layer of a nitride-based compound semiconductor, a light-emitting layer, and a p-type layer are formed in this order on a substrate, and a hydrogen-permeable electrode whose main constituent material is Pd is formed on the p-type layer. A method of manufacturing a light emitting element, comprising: forming an electrode pad made of a material that does not transmit hydrogen on a part of the hydrogen permeable electrode; and performing thermal annealing at a temperature of 600 ° C. or more and 900 ° C. or less. 5. A light emitting device manufactured by the manufacturing method according to claim 4, wherein the hydrogen permeable electrode is composed of two or more layers, and a side in contact with the p-type semiconductor is a Pd electrode,
A light emitting device, wherein the thickness of the metal on the Pd electrode is 20 to 200 °, and the total thickness of the Pd electrode and the metal is 40 to 400 °.